Two-stage hydraulic device

ABSTRACT

A master cylinder for hydraulic brakes has large and small cylinders arranged end-to-end in an integral cylinder housing, with large and small pistons which are structurally integral operating in the two cylinders and having unidirectional seals in contact with the cylinder walls, the small piston seal positioned to cut off a passage connected with a reservoir at the beginning of the two-stage working stroke. As pressure in the large cylinder increases, a relief valve opens in a passage in the piston, equalizing the pressure in the two cylinders so that the entire operator effort applies to the small cylinder only. Hydraulic pressure for braking is thus substantially increased with little increase in operator effort.

United States Patent [191 Hagberg, Jr.

[22] Filed:

Warren, Mich. 48093 Oct. 17, 1972 21 Appl. No.2 298,193

Related US. Application Data [63] Continuation-impart of Ser. No. 124,703, March 16,

1971, abandoned.

1,062,138 12/1953 France .60/54.6A

Apr. 9, 1974 Primary Examiner-Edgar W. Geoghegan Assistant Examiner-A. M. Zupcic Attorney, Agent, or Firm-Edward J. Kelly; Herbert Berl; John F. Schmidt ABSTRACT A master cylinder for hydraulic brakes has large and small cylinders arranged end-to-end in an integral cylinder housing, with large and small pistons which are structurally integral operating in the two cylinders and having unidirectional seals in contact with the cylinder .walls, the small piston seal positioned to cut off a passage connected with a reservoir at the beginning of the two-stage working stroke. As pressure in the large cylinder increases, a relief valve opens in a passage in the piston, equalizing the pressure in the two cylinders so that the entire operator effort applies to the small cylinder only. Hydraulic pressure for braking is thus substantially increased with little increase in operator ef- 1 Claim, 6 Drawing Figures TWO-STAGE HYDRAULIC DEVICE RELATED APPLICATIONS This application is a continuation-in-part of my copending application Ser. No. 124,703, filed Mar. 16, 1971 now abandoned, for a TWO-STAGE HYDRAU- LIC DEVICE, and I claim the filing date of that application for all common patentable subject matter.

The invention described herein may be manufactured, used, and licensed by or for the Government for governmental purposes without payment to me of any royalty thereon.

BACKGROUND OF THE INVENTION In the field of hydraulic actuation of mechanisms, there are numerous applications which require that the actuator move through a first operating stage which consists merely in overcoming distance under no-load, followed by a second operating stage during which the actuator works against substantial resistance to achieve the object of the entire operation. Examples of such an application are: a punch press for work-pieces which may vary in thickness, and it is desirable to move the punch as quickly as possible from its retracted or starting position to a position in contact with the work-piece and ready to begin the cut (or punch); and brakes, in which the no-load distance varies because of wear, and to minimize total braking time it is desirable to move the brake shoes as quickly as possible to the contact position where braking begins; other examples will be apparent to those skilled in the art.

1. Field of the Invention The invention relates to actuators for mechanisms which operate through a two-stage working stroke, the stroke being rectilinear, arcuate, angular, planar or three-dimensional, or a combination thereof; and consisting of two operating stages of which the first involves a no-load or light load movement which accomplishes little or nothing more than taking up the slack in linkage, moving a tool through a clearance space, or the like, and which should therefore be done speedily, and the second stage consisting of the actual accomplishment of the desired objective in which the actuator meets with the resistance that must be overcome. Fluid motors lend themselves readily to such applications, especially hydraulic devices of the piston-and-cylinder type wherein a piston-and-cylinder assembly can deliver hydraulic fluid in the volume and at the pressure required by the circumstances.

2. Description of the Prior Art It is known to use piston-and-cylinder devices which provide for automatic shift between large and small pistons depending on requirements. Examples are a "Power Brake Cylinder marketed by Stage-Matic Hydraulics, Inc., of 3316 Gorham Avenue, Minneapolis, Minn., and the master brake cylinder used on the Mercedes-Benz and described in Workshop Manual for Unimog-S Type 404", dated 1957 and published by Daimler-Benz Aktiengesellschaft, Gaggenau Plant. The prior art devices function to produce the two-stage effect discussed above, but have the disadvantage of complexity with the loss of reliability and the high cost that usually attend complexity. Moreover, as far as I have been able to determine, the prior art devices are not fail-safe devices, whereas a brake cylinder made according to this invention is a fail-safe mechanism as will be seen below.

SUMMARY OF THE INVENTION A two-stage piston-and-cylinder hydraulic pump in which the larger cylinder supplies fluid in substantial volume at comparatively low resistance to movement, and hence low pressure; after the actuator has taken up the no-load slack, the resistance to movement increases andconsequently the fluid pressure increases, whereupon a valve in the larger piston opens to by-pass fluid to a groove between the pistons. With the by-pass valve open, the force applied to the piston assembly moves the small diameter piston against the resistance at a consequently higher pressure.

OBJECTS It is an object of the invention to provide a master hydraulic cylinder which can deliver fluid at substantially no-load for rapid movement of the hydraulically actuated motor, and when the motor is loaded, automatically shift to supplying fluid at a substantially higher pressure.

It is a further object of the invention to provide a master cylinder which is simple in design, inexpensive to manufacture, and reliable in operation.

It is another object to provide a two-stage master cylinder which is just as operative as a single stage cylinder would be, if the high-pressure stage should fail for any reason.

In the Drawings;

FIG. 1 is a schematic drawing of a hydraulic system utilizing a master cylinder of the design proposed by this invention.

FIG. 2 is a longitudinal sectional view through the master cylinder shown in profile in FIG. 1 and depicting the parts in the fully retracted position.

FIG. 3 is a view similar to that of FIG. 2, but showing the parts in position for high pressure displacement by the small piston.

FIG. 4 is a longitudinal sectional view through a twoway check valve, being substantially a section on line 4-4 of FIG. 2.

FIG. 5 is a view in section substantially on line 55 of FIG. 1, but on alarger scale than FIGS. 2 and 3; and

FIG.-6 is a view in section on line 6-6 of FIG. 5 and on a larger scale than FIG. 5.

DESCRIPTION OF A PREFERRED EMBODIMENT FIG. 1 shows a hydraulic system having an actuator 2, which in the embodiment shown in a piston rod, connected to actuate a device 4 through two operating stages of which the first consists merely in overcoming the clearance between the friction surfaces of brake shoes 6 and drum 8 while overcoming the resistance of spring 10. This first operating stage is carried through under substantially no-load conditions.

Piston rod 2 is part of a hydraulic brake operating device 12 comprising a piston 14 and a cylinder 16 connected to a master cylinder 18 by means of a fluid conduit 20. A conventional brake lever 22 is mounted to apply a force F to a rod 24.

As is best seen in FIG. 2, a master power device 18 made according to this invention comprises a housing 26 forming a large cylinder 28 defining a pressure output chamber and a small cylinder 30 defining a pressure input chamber. The communicating internal sur- The connected pistons 36 and 38 present, respectively, a large piston cylindrical surface 40 and a small piston cylindrical surface 42 having a piston rod that defines an annular groove 44 between the pistons. The large piston cylindrical surface 40 is bounded at one end (the right end as shown in FIGS. 2 and 3) by an M nular face 46 and atits opposite end by an opposing face 48. As will be understood by those skilled in the art, the hydraulic pressure in the space between pistons 40 and 42 has a net effect on the annular surface which is thedifference between the area of piston 40 and the area of piston 42, whereas the hydraulic pressure acting on opposing face 48 acts on the entire area of piston 40 as long as the passage through the piston, detailed below, remains closed.

The free (and open) end 50 of large cylinder 28 is closed in any suitable manner by a cylinder head 52 which has a fluid-tight connection 54 with aforesaid conduit and an opening 56 through cylinder head 52.,At the inner end of opening 56 there is disposed a two-way check valve 58. Even though valve 58 is a readily available commercial item, for the sake of a complete disclosure this valve is functionally detailed in FIG. 4. As there shown, a cup-shaped housing 60 has a flanged seat 62 which is held against a gasket-washer 64 by a'spring 66 in compression between flanged seat 62 and opposing face 48 of large piston 36. At the bottom of cup 60, an opening 68 is provided. A gasket 70 is biased into position to seal opening 68 by a pressure plate 72, a spring 74 being in compression between pressure plate 72 and a perforated spring seat 75 secured in place in any suitable manner in the cup-shaped housing 60. I

Two-stage master hydraulic device 18 is provided with means for by-passing hydraulic fluid from large cylinder 28 to the space (groove 44) between pistons 36 and 38. More specifically, passage means communicate the space in cylinder28 between cylinder head 52 and opposing face 48 with the space between the pistons, said passage means comprising a passage 76 and passages 78. Passage 76 is here shown as a substantially central bore 80 formed in the integral two-piston structure from the opposing face 48 and having a bored valve seat element 82 threadedly engaging the open end of bore 80. A ball check element 84 is biased against the seat of element 82 by a spring 86 which is compressed between the ball and the inner, closed, end of bore 80. Passages 78 communicate bore 80 near its closed end with the surface of groove 44.

Cylindrical surfaces and 42 of pistons 36 and 38 are grooved as at 88 and 90 to receive unidirectional seals 92 and 94 respectively. A stabilizer 96 for the dual-piston structure is provided at the extreme right end as seen in FIGS. 2 and 3, spaced from piston 38 by a groove 98 and having a wiper 100 to minimize loss of hydraulic fluid out the open end 102 of small cylinder 30. A conventional closure disc 104 is held in a suitable counterbore in surface 34 by a snap ring 106. A socket 108 is provided in the end of the two-piston assembly to receive the end of rod 24.

A hydraulic fluid reservoir 110 is provided, preferably integral with housing 26. A fluid passage port 112 in the wall of small cylinder 30 connects the reservoir with the small cylinder. Passage 112 is disposed longitudinally such that it is cut off from communication with the cylinder bore by seal 94 as soon as the dual piston assembly begins its forward motion.

Inasmuch as seal 94 is unidirectional, permitting hydraulic fluid flow from right to left as seen in FIG. 2, the solution is to locate passage 112 for early cut-off by seal 94.

The unidirectional properties of both seals 92 and 94 is conventional, as is also the provision of generally longitudinal passages 114 and l 16 in pistons 36 and 38 immediately to the right of grooves 88 and 90, thus serving to communicate grooves 88 and with grooves 44 and 98 respectively. It is also conventional to place thin metal back-up rings between seals 92, 94 and passages 1 14, 116 respectively, to keep the seals from being extruded into the passages. Such back-up rings are not illustrated in the drawings.

In order to insure that hydraulic fluid may drain from the brake operating device 12 back to reservoir after pistons 36 and 38 have returned to the brakereleased position, I have provided depressurizing bypass means through piston 36. Such by-Pass means is shown in FIG. 5 as being approximately 90 from the plane of FIGS. 2 and 3, although it may be disposed wherever there is room for it.

The by-pass passage shown in FIGS. 5 and 6 can be one such passage means, and comprises a bore 1 18 and a larger, connecting, bore 120 communicating at their non-adjacent ends with faces 48 and 46 respectively of piston 36. Larger bore 120 receives a check valve which opens to permit flow from right to left but is normally closed to flow from left to right unless forcibly opened as the piston 36 returns to its retracted position. 1

More specifically, a valve seat element 112 is threaded into the right end of bore 120 and is bored to receive an actuator stem 124. A preferred such bore is shown in FIG. 6 as a spline 126, which permits fluid flow along stem 124 through the open splines. Element 122 carries a valve seat at its left end as seen in FIG. 5, and stem 124 carries a ball element 128 which is biased toward element 122 by a spring 130. In the brakeoff position of piston 36, stem 124 is adapted to engage the shoulder between bores 32 and 34 so as to push stem 124 leftward and unseat ball 128 against the bias of spring 130. Preferably the dimensions are such that there is very little travel of ball 128.

OPERATION .As lever 22 is actuated in a direction to apply the brakes, rod 24 moves the piston structure leftward as seen in FIGS. 2 and 3. Ball 84 is seated and remains seated during the first stage because of the force ex erted by spring 86. Large piston 36 pushes hydraulic fluid out through the two-way check valve 58 and conduit 20 to ram 12 (FIG. 1). Piston 14 moves to the right, driving device 4 between the brake shoes 6 and cumming them apart into contact with brake drum 8. During this movement of piston 36, seal 92 is effective to prevent significant fluid leakage from left to right past piston 36.

It will be noted that the volume of the space between pistons 36 and 38 is increasing during this phase of the operation. Reservoir 110 is vented to atmosphere, and fluid flows through passage 112 to prevent the existence of any significant sub-atmospheric pressure between the pistons. This is true even though passage 112 is covered by seal 94 before the brake shoes contact the brake drum, because seal 94 allows fluid to pass from right to left. In an extreme case, if there is very poor brake adjustment or has been considerable wear, the dual piston structure may even be to the left of the position shown in FIG. 3 before the brake shoes contact the drum, in which position fluid is drawn through the pas sages 116 to keep the space between the pistons filled with fluid.

As soon as the slack has been taken up in the system i.e., the brake shoes contact the drum further movement of the dual piston structure increases the pressure in the space between surface 48 and cylinder head 52, until the pressure is high enough to unseat ball 84. The pressure on the two sides of large piston 36 is thereupon substantially equalized, so that further leftward movement of the piston assembly has the effect of bringing small piston 38 to bear on the hydraulic fluid. During this phase or stage of operation, seal 94 is effective to stop pressure leakage from left to right past small piston 38. Continued pressure on rod 24 bi-. ases the piston structure leftward to move a smaller volume (virtually zero) of fluid out through conduit 20 at a substantially higher pressure. As will be understood by those skilled in the art, as soon as contact between the shoes and the drum is achieved, the system has little room for additional volume, and additional force applied to the piston structure serve primarily to increase the pressure in cylinder 28, conduit 20, and ram 12 (FIG. 1), thus increasing the resistance to rotation of drum 8 and, if pressure on rod 24 is maintained, eventually bringing drum 8 to a stop.

When the counterclockwise force on lever 22 is released, spring 10 pulls brake shoes 6 toward each other and away from contact with drum 8, pushing piston rod 2 and piston 14 to the left as seen in FIG. 1. This pushes hydraulic fluid back into cylinder 28 by way of conduit and two-way check valve 58. Because seals 92 and 94 are effective against flow to the right, pistons 36 and 38 move quickly to the right. If during this return stroke, pressure should build up in groove 44 to exceed the pressure to the left of seal 92, the seal would yield like a relief valve to permit pressure relief leftward past the seal. Hydraulic fluid will flow back to reservoir 1 10 via the by-pass means shown in FIG. 5, and passage 112 as necessary to accommodate the rightward shift of the dual piston structure.

Reference was made above to the fail-safe" characteristics of a master cylinder made according to this invention. lf spring 86 should suffer fatigue failure and break, or if for any reason ball 84 should fail to seat, the system would still function, although the brake pedal would then have to move through a greater distance.

Conversely, if ball 84 should be stuck in the closed position, and if ball 128 (FIG. 5) should be stuck open, the system would function to make the brakes operable by the application of a greater force to lever 22.

I wish it to be understood that I do not desire to be limited to the exact details of construction shown and described, for obvious modifications will occur to a person skilled in the art.

What is claimed is:

1. A mechanically-powered hydraulic pressure device comprising a small diameter piston operating in a small diameter pressure input chamber; a large diameter piston operating in a large diameter pressure output chamber, and a connecting rod rigidly joining the two pistons together for effecting a power stroke and a return stroke; a liquid supply reservoir communicating with the input chamber via a single flow port in the input chamber side wall; said small diameter piston having a first unidirectional peripheral seal riding on the input chamber side wall to move across the flow port during each stroke of the piston means so that the input chamber is in free open communication with the port when the piston means nears the end of its return stroke, and the peripheral seal is interposed between the input chamber and flow port when the piston means nears the end of its power stroke; said first peripheral seal being oriented so that when it is interposed between the input chamber and flow port it will permit flow from the reservoir through the port while preventing backflow from the input chamber through the port; said large diameter piston having a second unidirectional peripheral seal riding on the output chamber sidewall to permit flow from the input chamber into the output chamber while preventing backflow from the output chamber to the input chamber; pressureresponsive check valve means disposed in the piston means; said valve means being operable to permit flow from the output chamber to the input chamber when the pressure differential between said chambers reaches a predetermined value, whereby during the power stroke the piston means advances relatively rapidly until the output chamber is pressurized, after which the pressure-responsive check valve means opens to pressurize the input chamber for reducing the mechanical force that must be applied to the pistons to maintain the output chamber at a given state of pressurization; and a normally closed valve means carried by the large diameter piston for depressurizing the pressure output chamber at the end of the return stroke; said depressurizing valve means having an actuator arranged to contact an end wall of the output chamber to open the depressurizing valve means as the piston nears the end of its return stroke. 

1. A mechanically-powered hydraulic pressure device comprising a small diameter piston operating in a small diameter pressure input chamber; a large diameter piston operating in a large diameter pressure output chamber, and a connecting rod rigidly joining the two pistons together for effecting a power stroke and a return stroke; a liquid supply reservoir communicating with the input chamber via a single flow port in the input chamber side wall; said small diameter piston having a first unidirectional peripheral seal riding on the input chamber side wall to move across the flow port during each stroke of the piston means so that the input chamber is in free open communication with the port when the piston means nears the end of its return stroke, and the peripheral seal is interposed between the input chamber and flow port when the piston means nears the end of its power stroke; said first peripheral seal being oriented so that when it is interposed between the input chamber and flow port it will permit flow from the reservoir through the port while preventing backflow from the input chamber through the port; said large diameter piston having a second unidirectional peripheral seal riding on the output chamber sidewall to permit flow from the input chamber into the output chamber while preventing backflow from the output chamber to the input chamber; pressure-responsive check valve means disposed in the piston means; said valve means being operable to permit flow from the output chamber to the input chamber when the pressure differential between said chambers reaches a predetermined value, whereby during the power stroke the piston means advances relatively rapidly until the output chamber is pressurized, after which the pressureresponsive check valve means opens to pressurize the input chamber for reducing the mechanical force that must be applied to the pistons to maintain the output chamber at a given state of pressurization; and a normally closed valve means carried by the large diameter piston for depressurizing the pressure output chamber at the end of The return stroke; said depressurizing valve means having an actuator arranged to contact an end wall of the output chamber to open the depressurizing valve means as the piston nears the end of its return stroke. 